Problem with Web Applications

Web applications are stateless, means once a web page is rendered from server to client, nothing in the page remains on server and the next time user submits the page, the page will be called and created from scratch.

ASP.NET provides following solutions to solve this problem:

1- Viewstate
2- Session Variables
3- Application Variables
4- Cache
5- Cookies

Now the question arises that when to use what?

1- Viewstate

Viewstate is a hidden fields in an ASP.NET page, contains state of those controls on a page whose “EnableViewstate” property is “true”.
You can also explicitly add values in it, on an ASP.NET page like:
Viewstate.Add( “TotalStudents”, “87″ );
Viewstate should be used when you want to save a value between different round-trips of a single page as viewstate of a page is not accessible by another page.
Because Viewstate render with the page, it consumes bandwidth, so be careful to use it in applications to be run on low bandwidth.

2- Session Variable

Session variables are usually the most commonly used.
When a user visits a site, it’s sessions starts and when the user become idle or leave the site, the session ends.
Session variables should be used to save and retrieve user specific information required on multiple pages.
Session variables consumes server memory, so if your may have a huge amount visitors, use session very carefully and instead of put large values in it try to put IDs and references

3- Application variables

Application variables are shared variables among all users of a web application
Application variables behave like static variables and they are substitute of static variables as static variables are stateless in web applications
Only shared values should be persisted in Application variables, and as soon as they are not in use they should be removed explicitly.

4- Cache

Cache is probably the least used state feature of ASP.NET.
Cache is basically a resource specific state persistence feature, means unlike session it stick with resource instead of user, for instance: pages, controls etc.
Cache should be used or frequently used pages, controls, and data structures
Data cache can be used to cache frequently used list of values e.g. list of products

6- Cookies

Cookies are some values saved in browsers for a particular website o publicly accessible
The purpose of cookies is to help websites to identify visitors and retrieve their saved preferences
Cookies are also used to facilitate auto login by persisting user id in a cookie save in user’s browser
Because cookies have been saved at client side, they do not create performance issues but may create security issues as they can be hacked from browser

Finally remember the following points on your finger-tips:

1- Viewstate is bandwidth hungry
2- Session variables are memory hungry as per number of users
3- Applications variables are shared
4- Cache is memory hungry as per number of resources
5- Cookies are the least secure

Persistence Method	Who Needs the Data?	For How Long?	How Much Data?
Application	All users	Until the next application restart	Can be almost any size—it will only be stored once
Cookie	One user	As short as desired, or for months or even years if the user doesn’t delete their cookies	Minimal, simple data
Form Post	One user	For the next request (can be reused across many requests)	Virtually any size—the data is sent back and forth with every page
QueryString	One user or one group of users	For the next request (can be reused across many requests)	Minimal, simple data
Session	One user	As long as the user is active, plus a timeout period (typically 20 minutes)	Can be almost any size, but should be minimized since every user has their own separate session store
Cache	All users or a subset of users	As long or as short as needed	Can be used for large or small, simple or complex data
Context	One user	This request only	Can hold large objects, but typically does not since it is often used for every request
ViewState	One user	One Web form	Minimal; as with Form Post, this data is sent back and forth with every page
Config file	All users	Until the configuration file is updated	Can hold a lot of data; usually organized as many small strings or XML structures

For more information http://msdn.microsoft.com/hi-in/magazine/cc300437(en-us).aspx

One Response to “How to choose from Viewstate, SessionState, Cookies and Cache”

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   January 4, 2012 at 1:44 AM

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